The present invention relates to a swash plate type variable displacement compressor.
A conventional swash plate type variable displacement compressor Includes a cylinder block and a housing. The cylinder block defines a cylinder bore therein. The housing is fixed to the cylinder block and defines a crank chamber, a suction chamber and a discharge chamber. The suction chamber and the discharge chamber are connected to a refrigerating circuit that includes a condenser, an expansion valve and an evaporator. A piston is accommodated in the cylinder bore so as to be able to reciprocate therein. The piston defines a compression chamber in the cylinder bore. A drive shaft is rotatably supported by the cylinder block and the housing. The drive shaft is driven by an external drive source such as an engine of a vehicle. A swash plate is supported by the drive shaft in the crank chamber so as to rotate integrally with the drive shaft and so as to be inclinable with respect to the axis of the drive shaft. The swash plate allows the piston to reciprocate through a pair of shoes and a piston rod. The pressure in the crank chamber is controlled by a control mechanism,
There are three types of the control mechanisms. One of the control mechanisms, which is a supply control mechanism, includes a bleed passage that has a constant inner diameter and continuously interconnects the crank chamber with the suction chamber regardless an inclination angle of the swash plate, and adjusts an opening degree of a supply passage which interconnects the discharge chamber with the crank chamber by a control valve. Another control mechanism, which is a bleed control mechanism, adjusts an opening degree of the bleed passage by a control valve. The other control mechanism, which is a three-way valve control mechanism, adjusts both opening degrees of the bleed passage and the supply passage by a control valve.
In the compressor, when the drive shaft is driven by the external drive source, the swash plate rotates integrally with the drive shaft. The piston reciprocates in the cylinder bore in accordance with the inclination angle of the swash plate. Refrigerant gas is introduced from the suction chamber into the compression chamber. The refrigerant gas is discharged to the discharge chamber after compressed. Therefore, refrigeration capacity in the refrigerating circuit is performed in accordance with an amount of the refrigerant gas discharged to the discharge chamber. Since the pressure in the crank chamber is controlled by the control mechanism, the inclination angle of the swash plate is adjusted. As a result, the stroke of the piston is varied, and the amount of the refrigerant gas discharged from the compression chamber to the discharge chamber by the reciprocation of the piston is varied.
In the control mechanism, blow-by gas, which is the refrigerant gas leaked from the compression chamber through a clearance between the cylinder bore and the piston, is supplied to the crank chamber. In the control mechanism including the supply passage, high-pressure refrigerant gas is supplied from the discharge chamber to the crank chamber. On the other hand, in the control mechanism including the bleed passage, the refrigerant gas in the crank chamber is discharged to the suction chamber. The refrigerant gas includes lubricating oil. Therefore, the lubricating oil is stored in the crank chamber, and sliding parts such as the swash plate and the shoes are lubricated by the lubricating oil.
However, in the above-mentioned swash plate type variable displacement compressor, the lubricating oil is excessively stored in the crank chamber in the maximum displacement operation of the compressor, depending on a kind of the control mechanisms. In this case, it is hard to cope with the compression efficiency and the durability of the compressor.
Namely, in the compressor including the supply control mechanism as the control mechanism, the inner diameter of the bleed passage is small so as to be able to increase the pressure in the crank chamber in a displacement-decreasing operation of the compressor, in which the supply passage is opened by the control valve for decreasing the displacement of the compressor. Furthermore, in the maximum displacement operation of the compressor, in which the pressure in the crank chamber is relatively low, the supply passage is closed by the control valve. So the high-pressure refrigerant gas in the discharge chamber is not supplied to the crank chamber. Therefore, in the maximum displacement operation of the compressor, the lubricating oil stored in the crank chamber is not pushed out to the bleed passage by the refrigerant gas. As a result, the lubricating oil is excessively stored in the crank chamber.
Also, in the compressor including the three-way valve control mechanism as the control mechanism, when the displacement of the compressor is decreased by increasing the pressure in the crank chamber, the supply passage is opened by the control valve and the bleed passage is closed by the control valve. On the other hand, when the displacement of the compressor is increased by decreasing the pressure in the crank chamber, the supply passage is closed by the control valve and the bleed passage is opened by the control valve. Therefore, the opening degree of the bleed passage, which becomes the maximum by the control valve in the maximum displacement operation of the compressor, is not relatively large. Furthermore, in the maximum displacement operation of the compressor, the supply passage is closed, and the high-pressure refrigerant gas in the discharge chamber is not supplied to the crank chamber. Therefore, in the maximum displacement operation of the compressor, the lubricating oil stored in the crank chamber is hard to push out to the bleed passage by the refrigerant gas. The lubricating oil is easily excessively stored in the crank chamber. Although the three-way valve control mechanism includes the bleed passage, the lubricating oil is easily excessively stored in the crank chamber due to a small inner diameter of the bleed passage.
On the other hand, in the compressor including the bleed control mechanism as the control mechanism, the pressure in the crank chamber is increased by the blow-by gas that is continuously supplied to the crank chamber and by the high-pressure refrigerant gas that is continuously supplied to the crank chamber through the supply passage. Therefore, in the maximum displacement operation of the compressor, the opening degree of the bleed passage is large. As a result, the lubricating oil is hard to store in the crank chamber excessively.
When the control mechanism is the supply control mechanism or the three-way valve control mechanism, in the maximum displacement operation of the compressor, the lubricating oil is excessively stored in the crank chamber. Therefore, the ratio of the lubricating oil in the refrigerant gas is decreased in the refrigerating circuit, and the refrigerant gas that does not contain much lubricating oil is introduced from the suction chamber into the compression chamber. As a result, sliding performance of the piston in the cylinder bore may deteriorate, and it is worried that the durability of the piston deteriorates.
In order to solve the above problem, it is considered to increase the ratio of the lubricating oil in the refrigerant gas. However, in the compressor, in the displacement-decreasing operation of the compressor, in which the pressure in the crank chamber is relatively high, the supply passage is opened by the control valve. The high-pressure refrigerant gas is supplied to the crank chamber, and the lubricating oil stored in the crank chamber is easily pushed out to the bleed passage by the high-pressure refrigerant gas. Therefore, if the ratio of the lubricating oil in the refrigerant gas is increased, a large amount of the lubricating oil, which is pushed out in the displacement-decreasing operation of the compressor, is mixed in the refrigerant gas in the refrigerating circuit. The ratio of the lubricating oil in the refrigerant gas in the refrigerating circuit becomes excessively high. As a result, the compression efficiency of the compressor becomes low.
A communication path that interconnects the crank chamber with the compression chamber is disclosed in Japanese Unexamined Patent Publication No. 56-162281, No. 7-35037, No. 2001-107847 and No.2001-20863, and International Publication No. WO96/39581.
In the compressor disclosed in Japanese Unexamined Patent Publication No. 56-162281, a swash plate is fixed to a drive shaft and is not inclinable with respect to the axis of the drive shaft. The compressor does not include a control mechanism that controls the pressure in the crank chamber for changing the displacement of the compressor. In the compressor, which is a fixed displacement type, only volumetric efficiency is improved by interconnecting the crank chamber or a swash plate chamber with the compression chamber by the communication path.
In the compressor disclosed in Japanese Unexamined Patent Publication No. 7-35037, refrigerant gas in the crank chamber is introduced into the compression chamber through the communication path that interconnects the crank chamber with the compression chamber. Lubricating oil in the crank chamber is not discharged into the compression chamber in the maximum displacement operation of the compressor. The communication path only allows the refrigerant gas to move from a suction chamber to the crank chamber, and the pressure in the crank chamber is not decreased through the communication path.
In the compressor disclosed in Japanese Unexamined Patent Publication No. 2001-107847, the communication path that interconnects the crank chamber with the compression chamber functions as a passage for blow-by gas. Lubricating oil in the crank chamber is not discharged into the compression chamber in the maximum displacement operation of the compressor.
A compressor in which a groove is formed on the outer circumferential surface of the piston is disclosed in Japanese Unexamined Patent Publication No. 2001-20863 and International Publication No. WO96/39581. However, in the compressor disclosed in Japanese Unexamined Patent Publication No. 2001-20863, the groove does not interconnect the crank chamber with the compression chamber and only functions as a fluid bearing. Also, in the compressor disclosed in International Publication No. WO96/39581, the groove does not interconnect the crank chamber with the compression chamber and is only for storing the lubricating oil in a cylinder bore therein.